Abstract: In transformer routine tests, the dielectric loss factor of casing test is a routine test, the actual operation equipment especially dry casing pipe dielectric loss test unqualified in most cases are caused by the internal casing be affected with damp be affected with damp, but there is a kind of dry type casing dielectric loss data exception is caused by casing dielectric polarization resistance current cause the dielectric loss value increase, This kind of anomaly usually shows that the dielectric loss value decreases with the increase of external test voltage, but the capacitance value does not change all the time.This paper discusses the treatment process of this kind of defect in actual equipment, and puts forward the treatment method of this kind of problem.